Logo design is an important area of graphic design, and one of the most difficult to perfect. The logo (ideogram), is the image embodying an organization. Because logos are meant to represent companies' brands or corporate identities and foster their immediate customer recognition, it is counterproductive to frequently redesign logos.
Color is considered important to brand recognition, but it should not be an integral component to the logo design, which could conflict with its functionality. Some colors are formed/associated with certain emotions that the designer wants to convey. For instance loud primary colors, such as red, are meant to attract the attention of drivers on highways are appropriate for companies that require such attention. In the United States red, white, and blue are often used in logos for companies that want to project patriotic feelings. Green is often associated with the health and hygiene sector, and light blue or silver is often used to reflect diet foods. For other brands, more subdued tones and lower saturation can communicate reliability, quality, relaxation, or other traits.
Article Source: http://en.wikipedia.org/wiki/Logo